This invention relates to an air- and/or oven-drying lubricant paint composition for producing dry-film lubricants, especially for bolts and screw connections.
Structural parts of any type that are in movement relative to each other during their use must be lubricated appropriately to reduce the frictional resistance and the wear that it causes. Permanent lubrication in the form of dry-film lubricants based on solid lubricants has proven to be especially advantageous for parts that are exposed to oscillating or intermittent movements.
With regard to the theory and practice of solid lubricants, the reader is referred to Ingenieur Digest, Vol. 13, No. 12 and Vol. 14, Nos. 1 to 3, by Dr. Fritz Wunsch (Kluber Lubrication Munich KG). This publication gives a survey of the most important lubricants, their mode of action, the commercial forms in which they are available and their use.
In particular, this review describes organic lubricant paints that can contain primarily molybdenum disulfide and graphite or polytetrafluoroethylene as the solid lubricant pigment and a polyimide resin as a binder.
A similar composition is also described in Journal of the American Society of Lubrication Engineers (1967) pp. 288-294, where lubricant paints are described that contain molybdenum disulfide or antimony trioxide as solid lubricant pigments, polyimide resins as binders and N,N-dimethylacetamide or mixtures of pyrrolidone and xylene as the solvent together with an extender.
The above lubricant paints of the art for forming dry-film lubricants can be used for a wide variety of lubrication purposes; so, theoretically, they can also be used to lubricate screw connections in order to at least bring the friction conditions at the head and thread of the screw under some control, because this causes prestressing of the screw connections. There is generally a reduction in the coefficient of friction when a screw connection is lubricated in this way. However, in addition to the reduced coefficient of friction, screw connections lubricated in this way generally experience a number of other problems.
Thus, special thread lubricants have been developed specifically to better meet the special requirements of screw connections. In this regard, especially suitable high-performance lubricants and the special conditions prevailing in the lubrication of screw connections are discussed in the brochure, Empirical Reports, 46/1, Screws, 2/III/67, from the company Molykote. According to this report, a particular problem encountered in lubricating screw connections is that there is generally a reduction in the coefficient of friction, but there is a wide range of variation in this reduction with different carrier metals and with different surface treatment methods, and a great deal of scattering between one screw and another within the same production lot. In addition, there is also a relatively great scattering in the coefficient of friction after repeated loosening and tightening of a given screw connection.
This fact is recognized as a major problem in the industry, so there is an urgent need for providing more security for screw connections. There is also the closely related problem of the loosening of screw connections due to vibration, which exists with a wide variety of structures, and especially in the automobile industry.
A lubricant paint for forming dry-film lubricants, especially for bolt and screw connections, would be ideal (i) if it provided a reduction in the coefficent of friction to a practically uniform and relatively narrow range for a wide variety of carrier metals and surface treatment methods and within the same production lots, (ii) if it would show practically no scattering in the coefficient of friction after repeated loosening and tightening of the screw connection, and (iii) if it would nevertheless yield a screw connection that would resist loosening, especially under vibration. None of the lubricant paints known so far does justice to this ideal to any extent at all.